Heat-exchange means



Aug. 2, 1966 MOKAY 3,263,747

HEAT-EXCHANGE MEANS Filed April 21, 1965 Gordon McKay mvsmoa United States Patent 3,263,747 HEAT-EXCHANGE MEANS Gordon McKay, Southampton, England, assignor to Esso Research and Engineering Company, a corporation of Delaware Filed Apr. 21, 1965, Ser. No. 449,696 Claims priority, application Great Britain, Apr. 1, 1960, 11,629/ 60 4 Claims. (Cl. 165-76) This application is a continuation-in-part of applicants prior copending application Serial No. 97,203 filed March 21, 1961, now abandoned.

This invention relates to improvements in the construction of air heaters, and particularly relates to an improved form of heat-exchange tube for use in air heaters.

Boiler installations generally employ a plurality of heat-exchange systems of tube elements disposed in a stream of hot combustion gases. Thus gases from the main boiler unit may pass in turn to a superheat unit, a hot water unit, and an air-heating unit. The hot sulfurcontaining gases passing through the air-heating unit are generally below their dew-point at the outgoing end of the unit, and a long-standing problem has been the formation of corrosion deposits and general fouling on the outside of the tubes exposed to the hot gases. The conventional method of construction of tube assemblies is to fix the ends of each heater tube in perforations in each end-plate supporting the tube array. Expansion effects in such tube arrays are taken up by bowing of the tubes and drumming of the end-plates. It is an inherent defect in such constructions however in that the tube forms an integral part of the end-plates, and the tubes after use cannot be removed for descaling. Thus when the heatexchange etficiency falls below an acceptable level, the air-heater unit has to be removed, and a new one inserted into the system.

A new form of heat-exchange construction of the type employing heat-exchange tubes has now been devised which allows easy removal and replacement of heatexchange tubes and further allows the use of fragile or brittle material for the heat-exchange tubes, and avoids the generation of stresses within such tubes due to thermal expansion elfects. In particular, heat-exchange tubes according to this invention may be fabricated from heatresistant glass, e.g. a boro-silicate type of glass. Besides being resistant to the corroding effect of sulfur-containing flue gases at temperatures below their dew-point, the smooth glass surfaces allow soot or other ash deposited thereon to be cleared easily.

Heat-exchange units according to this invention are characterized in that the heat-exchange tubes are not rigidly attached to both the end-plates supporting the tubes, but that an external lip portion of one end of the tubes bears against one tube-plate, the tubes passing through perforations in the said end-plate, and resting in corresponding perforations in a further end-plate situated at the other end of the tube. Thus forces are not generated in the tubes due to the thermal expansion thereof, but the tubes are adapted for free movement in the perforation in the said further end-plate.

Tube assemblies according to this invention may be in a vertical array, in which instance the tubes may hang by their external lips in the perforations in the first endplate, or they may be in a horizontal array, in which instance tube-retaining means may be clamped on the lipped ends of the tubes to enable them to bear against the end-plate. If desired, the tube-retaining means may be applied to the lipped tubes in a vertical array to damp down movement of the tubes due to vibration or the like. In practice it is desirable to employ sealing means between the exterior of the tubes and the rim of the perforations to preserve a gas-tight seal during movement of the tubes within the perforations.

Heat-exchange tubes according to this invention thus comprise a tube of heat-resistant material of substantially constant bore and having an external lip at one end of the tube adapted to bear against an adjacent tubeplate containing the heat-exchange tube.

The use of tubes of substantially constant bore avoids a pressure drop of gases flowing Within the tube. Thus if a pinched tube is employed, a venturi effect is obtained when gases flow through the tube, resulting in a substantial pressure drop when a plurality of tubes are used. It is particularly preferred that the tubes be constructed of fire-resistant glass, or of alumina.

While the improved tubes and heat-exchange tubes according to this invention have been described in relation to air-heaters, it Will be appreciated that the improved tubes may be used in heat-exchange units of other systems.

Embodiment of the invention will now be described and illustrated in the accompanying drawings wherein:

FIG. 1 is a perspective view of a heat-exchange tube according to this invention;

FIG. 2 is a vertical cross-section of one tube inserted in a vertical array according to this invention;

FIG. 3 is an elevation of four tubes in a horizontal array according to this invention; and

FIG. 4 is a cross section showing an alternate form of tube securing means.

Referring to FIG. 1, a boro-silicate tube 1 of substantially uniform bore has a lip portion 2 at one end of the tube 1 having a fiat undersurface 3 adapted to bear against a tube-plate when the tube is placed adjacent the tubeplate.

In FIG. 2 a heat-exchange tube (as shown in FIG. 1) according to this invention is designated 21 and suspended by its lip 22 through a perforation in a first tubeplate 23, and extends through a corresponding perforation in a second tube plate 24. An asbestos packing gasket 25 of annular L-shaped cross-section is inserted between the tube lip 22 and the apertures in the tube-plates 23 and 24 to provide a substantially gas-tight seal, and to allow free movement of the tube 21 through the aperture in the tube-plate 24.

In FIG. 3 four heat-exchange tubes according to the invention 31 are disposed in horizontal array within perforations within the tube-plate 33. External lipped portions 32 of the tubes 31 abut against the external surface of the plate 33, and are held thereto by a washer 34 bearing against the lips 32 and secured to the plate 33 by screw 35.

FIG. 4 is similar to FIGS. 2 and 3 but shows an alternate form of tube securing means. In FIG. 4 a stud 41 is welded or otherwise secured at 42 to the exterior surface of tube-plate 23. The stud includes a shoulder 43 against which a flexible spring washer 34a is held by a spring C clip generally designated 44. The location of the shoulder 43 relative to the outer surface of the tube lip is selected so that the spring washers will maintain a steady bias to hold the tube lips in tight pressing contact with the underlying lips of the gaskets 25 irrespective of minor changes in dimension that may occur in the thickness of the gasket 25.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An improved heat exchanger for heating air with hot products of combustion containing corrosive gases near their dew-point comprising, in combination; a structure defining a first gas passageway for said hot combustion products, said structure including opposite wall portions, each having a plurality of apertures in substantial alignment with the apertures in the wall portion opposite thereto; a plurality of heat-and corrosion-resistant glass tubes extending transversely across said first gas passageway and through said apertures to thereby form a second passageway for the flow of gas to be heated in said heat exchanger, each of said glass tubes having a body portion of uniform outside diameter throughout its length, said diameter being substantially less than the diameter of said apertures to form an annular space therebetween and an annular end lip portion exterior of said first passageway and of outside diameter greater than the diameter of said apertures and of said body portion, and heatresistant resilient gasket means mounted in the annular space between the tube body portion and the apertures to form a substantially gas-tight seal around each tube end while permitting relative longitudinal movement of the tubes with respect to the end plates, at least said gasket means at the lip end of said tube having an enlarged aunular flange extending between the tube lip portion and the adjacent wall portion, and means exterior of said first passageway for holding the lip portion of each tube in 2. The combination according to claim 1 wherein said holding means includes a single clamping element to hold a plurality of adjacent tube lip portions.

3. The combination of claim 2 wherein said gasket means at each end of each tube is substantially identical in shape.

4. The combination according to claim 2 wherein said holding means includes a stud secured to an exterior surface of said first passageway adjacent said tube lip portions, a circular spring washer having an aperture therein disposed over said stud with the periphery of said washer overlying at least two adjacent lip portions, and means holding said spring washer upon said stud for creating an axial spring bias force against said tube lip portion and underlying gasket means whereby a substantially gastight seal will be maintained irrespective of small dimensional changes in the thickness of the annular flange of said gasket means.

References Cited by the Examiner UNITED STATES PATENTS 1,781,913 11/1930 Batter -59 2,577,120 12/1951 Franz 285-137 FOREIGN PATENTS 62,677 2/1955 France.

R. A. OLEARY, Primary Examiner.

CHARLES SUKALO, Examiner. 

1. AN IMPROVED HEAT EXCHANGER FOR HEATING AIR WITH HOT PRODUCTS OF COMBUSTION CONTAINING CORROSIVE GASES NEAR THEIR DEW-POINT COMPRISING, IN COMBINATION; A STRUCTURE DEFINING A FIRST GAS PASSAGEWAY FOR SAID HOT COMBUSTION PRODUCTS, SAID STRUCTURE INCLUDING OPPOSITE WALL PORTIONS, EACH HAVING A PLURALITY OF APERTURES IN SUBSTANTIAL ALIGNMENT WITH THE APERTURES IN THE WALL PORTION OPPOSITE THERETO; A PLURALITY OF HEAT-AND CORROSION-RESISTANT GLASS TUBES EXTENDING TRANSVERSELY ACROSS SAID FIRST GAS PASSAGEWAY AND THROUGH SAID APERTURES TO THEREBY FORM A SECOND PASSAGEWAY FOR THE FLOW OF GAS TO BE HEATED IN SAID HEAT EXCHANGER, EACH OF SAID GLASS TUBES HAVING A BODY PORTION OF UNIFORM OUTSIDE DIAMETER THROUGHOUT ITS LENGTH, SAID DIAMETER BEING SUBSTANTIALLY LESS THAN THE DIAMETER OF SAID APERTURES TO FORM AN ANNULAR SPACE THEREBETWEEN AND AN ANNULAR END LIP PORTION EXTERIOR OF SAID FIRST PASSAGEWAY AND OF OUTSIDE DIAMETER GREATER THAN THE DIAMETER OF SAID APERTURES AND OF SAID BODY PORTION, AND HEATRESISTANT RESILIENT GASKET MEANS MOUNTED IN THE ANNULAR SPACE BETWEEN THE TUBE BODY PORTION AND THE APERTURES TO FORM A SUBSTANTIALLY GAS-TIGHT SEAL AROUND EACH TUBE END WHILE PERMITTING RELATIVE LONGITUDINAL MOVEMENT OF THE TUBES WITH RESPECT TO THE END PLATES, AT LEAST SAID GASKET MEANS AT THE LIP END OF SAID TUBE HAVING AN ENLARGED ANNULAR FLANGE EXTENDING BETWEEN THE TUBE LIP PORTION AND THE ADJACENT WALL PORTION, AND MEANS EXTERIOR OF SAID FIRST PASSAGEWAY FOR HOLDING THE LIP PORTION OF EACH TUBE IN FIXED RELATIONSHIP WITH RESPECT TO THE SUPPORTING ADJACENT WALL PORTION WHILE PERMITTING RELATIVE LONGITUDINAL MOVEMENT OF THE OTHER END OF SAID TUBE WITH RESPECT TO THE OTHER WALL PORTION WHEREBY UPON RELEASE OF SAID HOLDING MEANS SAID TUBES MAY BE READILY WITHDRAWN FROM SAID FIRST GAS PASSAGEWAY FOR CLEANING AND INSPECTION. 